The known art describes microfluidic metering apparatuses that meter a single volume of fluid from an input volume of fluid. The known art is limited in operational functionality as it requires an additional, often mechanical, means to meter off a small volume of fluid, such as by using air pressure to force a known volume of liquid away from a larger volume of liquid. The prior art also does not adequately isolate the input volume of fluid from the metered fluid, which increases the possibility of contamination and inaccurate metering.
Patent Blatt et al. U.S. Pat. No. 4,761,381 (issued Feb. 26, 1987) discloses a device where, once a reaction chamber is filled via capillary action, excess fluid will flow through another capillary channel into an overflow chamber. The chambers are configured to try to prevent fluid flowing from the overflow channel back into the reaction chamber. Excess fluid in the overflow chamber is not held securely within the overflow chamber and could either leak out of the vent hole in the chamber, thus contaminating the device, or leak back into the reaction chamber if the device is moved during operation. Furthermore, Blatt et al. does not disclose the ability to passively meter a second volume of fluid from a passively metered first volume of fluid.
Patent Charlton et al. U.S. Pat. No. 5,208,163 (issued Dec. 6, 1991) discloses a method of self-metering fluid within an analysis device. A sample is introduced into the device via an entry port, which fills a metering chamber and access hole. A filter acts as a wick to draw blood into a reaction chamber, which comprises an absorbent membrane. Once the absorbent membrane is saturated, excess fluid is drawn down a metering capillary channel. The metered volume of fluid in this device is absorbed into an absorbent membrane and thus is not in free liquid form. Charlton et al. does not disclose the ability to accurately passively meter a first volume of fluid, and then passively meter a second volume of fluid from the first volume of fluid, where the second volume of metered fluid is maintained in a liquid form. Furthermore, Charlton et al. does not adequately prevent any excess fluid from re-entering the reaction chamber if the device is moved.
Patent Besemer et al. EP0392851B1 (issued Oct. 17, 1990) discloses a dilution and mixing cartridge that uses capillary flows and gravity to control the flow of fluid into a cartridge. Input fluid flows vertically down an input channel into a metering channel. Excess fluid then drains into an overflow channel. However, the device can only be operated in an upright position. Besemer et al. does not disclose the ability to passively meter a second volume of fluid from a passively metered first volume of fluid.
Patent Miller US 2012/0142020A1 (issued Dec. 1, 2011) discloses a sample metering and assay device with integrated sample dilution. A liquid sample is introduced through a sample entry port and capillary, which fills an input channel up to a capillary stop. The input port is sealed, and a second fluid is injected at a specific point along the input channel which meters off a small portion of the input sample. Miller does not disclose the ability to passively meter a second volume of fluid from a passively metered first volume of fluid.
While the known art discloses the use of capillary flows to meter a defined volume of fluid from an input volume of fluid, the art does not disclose the ability to sequentially passively meter a first defined volume of fluid from an input fluid, and then passively meter a second volume of fluid from the first metered volume of fluid, wherein all the excess fluid, in both metering steps, is absorbed by absorbent material leaving a defined volume of fluid in a fluidic channel. Thus, the prior art is limited in terms of both its accuracy, and its ability to further manipulate the second metered volume of fluid.